Electron coupling system, coupling through the envelope wall of discharge device by electromagnetic coupling



Sept. 27, 1966 ADLER 3,275,880

ELECTRON COUPLING SYSTEM, COUPLING THROUGH THE ENVELOPE WALL 0F DISCHARGE DEVICE BY ELECTROMAGNETIC COUPLING Filed Dec. 21, 1963 N E FQF I... b 1 A H m INVENTOR.

United States Patent 3,275,880 ELECTRON COUPLING SYSTEM, COUPLING THROUGH THE ENVELOPE WALL OF DIS- CHARGE DEVICE BY ELECTROMAGNETIC COUPLING Robert Adler, Northfield, 111., assignor to Zenith Radio Corporation, Chicago, Ill., a corporation of Delaware Filed Dec. 21, 1962, Ser. No. 246,468 3 Claims. (Cl. 315-4) The present invention pertains. to an electron coupling system and has particular reference :to a system for use with an electron beam parametric amplifier.

In the copending application of Robert Adler, Serial No. 119,931, filed June 27, 1961, entitled, Electron Beam Amplifiers and Apparatus Therefor, and assigned to the same assignee as the present application, there are disclosed a varietyof signal amplifying devices. In general these devices include an electron source for projecting an electron beam along a predetermined path terminating in a collector. Spaced along the beam path between source and collector are several components including a first beam energy interaction device or electron coupler disposed along the first portion of the path and respon sive to applied signal energy for coupling this energy to the electron beam. Next along the path toward the collector are means for stripping noise from the beam which is at the idler frequency and which is explained in detail in the above-mentioned application. Further along the beam path are means for expanding the energy which has been coupled to the beam by the first component. This means is commonly referred to as a pump. Lastly, a second coupler, which may be similar to the first coupler, is provided to extract amplified energy from the beam. This combination results in a device which parametrically amplifies electron signal motion. Since the present invention has found valuable utility in such devices, it will be described in that connection.

Parametric type amplifierspresently find their major use in microwave frequency applications. Suitable apparatus must be provided to couple such high frequency energy to external circuitry. The coupling circuits must have relatively low values of capacitance and inductance. At frequencies in the region of, for example, two kilo-megacycles it becomes increasingly difficult to maintain the reactance of the coupling apparatus at the desired low value.

Accordingly, it is an object of this invention to provide an improved electron coupling system in apparatus of the general kind described.

It is a more specific object of this invention to provide a coupling system which has a relatively low reactance in accordance with the requirements discussed above.

Still another object of the invention is to provide a new and improved coupling system which may be simply and economically constructed.

In accordance with the invention an electron coupling system comprises an envelope of low magnetic loss material which contains an electron source for projecting an electron beam along a predetermined path within the envelope. A coupler having a predetermined reactance is disposed in the envelope along the beam path for transferring energy of a predetermined frequency between the beam andcoupler. A plurality of transmission lines are provided, each with one end electrically connected to the coupler and the other end of at least two of the lines terminated in a common inductive element. The magnetic field around the common inductive element is substantially stronger than elsewhere along the transmission lines. The element is positioned in close proximity to the envelope. The transmission lines have respective lengths which produce an equivalent reactance at the ends connected to the coupler for placing the coupler in a resonant Patented Sept. 27, 1966 condition at the predetermined frequency. Finally, there are means having an inductive member situated outside of the envelope for coupling to the magnetic field of the common element, for inductively transferring energy at the predetermined frequency between the common ele ment and the inductive member through the envelope.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is an elevational view, partially broken away, of an amplifier constructed in accordance with the present invention;

FIGURE 2 is a fragmentary cross-sectional view taken along line 22 of FIGURE 1;

FIGURE 3 is an enlarged view of a portion of the apparatus shown in FIGURE 1;

FIGURE 4 is a perspective view, partially in crosssection, of a portion of FIGURE 2'; and

FIGURE 5 is a schematic representation of a portion of the structure shown in FIGURE 1.

Referring to FIGURE 1' which serves to illustrate the present invention, enclosed within an evacuated envelope 10 are an electron gun 11, first and second input couplers 12 and 13 disposed in a first beam path portion ibeyond gun 11, a parametric electron motion expander 14 dis posed in a second beam path portion beyond the first and an output coupler 15 disposed in a third path portion beyond expander 14, and a collector 16. In operation, the entire electron beam path is subjected to a longitudinal magnetic field which is most conveniently developed by means of a solenoid (not shown) within which envelope 10 is coaxially disposed.

Electron gun 11 is designed to develop and project along the beam path a pencil-like stream of electrons at least approximating a condition of Brillouin flow. To this end, the gun includes a cathode 18 followed by a series of annular electrodes 19. The electrons projected along the beam path from gun 11 are finally intercepted by collector 16 after passing suppressor electrode 20. The average axial velocity of the electrons is adjusted by the potential applied to the elements in each of the intermediate sections 12-15.

The parametric amplifier tube in which the invention is incorporated for'purposes of illustration has an envelope 10 of low magnetic loss material, in this instance of glass. Cylindrical shields 21, 22 and 23-which house input sections 12 and 13 and output section 15, respectively, are positioned adjacent the internal wall of envelope 10.

Input electron coupler 12 is surrounded by shield 21 except for a window 25. It has outwardly facing channellike electrodes 26 disposed on opposite sides of the electron beam path from cathode 18. An inductive loop 27 .and a tuning inductor 28 are connected across electrodes 26 with loop 27 disposed in window 25. Conducting walls 29 and 30 are disposed on each end of circumferential shield 21 to almost wholly enclose input coupler 12. Central apertures in walls 29 and 30 allow passage of the electron beam therethrough and a cylindrical guide channel 31 attached to wall 30 serves to prevent defocusing of the electron beam.

Input section 13' is an electron coupler which interacts with the beam electrons at a desired interaction frequency. Two conductive strips 32 and 33 (FIGURES 1, 2, and 3) are interleaved and wound coaxially about the beam path to form a bifilar helix coaxial with the path. Strip 32 is electrically and mechanically connected at three points to a cross member 34 which bisects and is afiixed to a rectangularframe 35, and similarly strip 33 is connected to, cross member 36 which bisects" rectangular support frame 37. Ends 34a, 36a of the cross,

members serve asone pair of terminals for the coupler and ends34b, 36b as the other pair. Frames 35 and 37 are permanently spaced from'one another by cross elements 38 and 39 which are fastened to the tops and bottoms of the .frames. The entire frame assembly'is supported on insulating spacers 40. through which studs 41, afiixed to the frames, extend..Frame assembly 35, 37 for coupler 13 embodies the novel concept of this invention and will be discussed in;detail below.

The frequency at which coupler 13 interacts withvthe beam electrons is a function of its pitch and direction of twist relative to the periodicity and direction of the resonant electron motion. A more complete explanation of this coupler will be found in the above-mentioned Adler application Serial No. 119,931. .1

- Expander section 14 may take the form of any devi appropriate to parametn'cally amplify the signal energy';

ductive discs46' which constitute the principal inductance to cause the quadrupole to resonate at a desired frequency. A pair of straps 47, as explained in the above;

application,-are provided to make certain the structures are excited in their desired mode.

Output coupler 15 is essentially identical .to input coupler 12 and will not be further described.

The entire assembly is' supported in envelope -by means of four ceramic rods 50 symmetrically disposed about the beam path and extending throughout all of the various apertured electrodes, shield walls, etc. The

different electrodes. are separated by ceramic washers 51 as best shown in FIGURE 2. The assembly is held tightly together by means of compression springs 52 disposed at .opposite ends of rods 50 under washers -53 pinned to the ceramic rods. The internal leads extend between the various electrodes and the different connector pins projecting through the base presses of envelope 10.

The manner in which input and output couplers 12 and interactwiththe electron beam, the action of coupler 13 in stripping idler noise from the beam and the action of expander 14 in amplifying the electron signal motion together with the related theory is fully discussed in the literature, including an article by RobertAdler et al.

that figure, coupling strips 32,133 are represented by 'an t equivalent capacitanceand frames 35 iand 37 by two.

pairs'of balanced transmission lines. Each line: has one end electrically connected to the equivalent capacitor, the lower case lettering, a-d, indicating the equivalence of each transmission line section to a section of frames 35 and 37. Theother end of-each pair of lines is joined. together in a common short circuit element; more specifif' cally, element 38 terminates *lines a, b and element 39 terminates lines 0,; d. The common elements are shown as divided into two parts in FIGURE 5.

a mission lines is made slightlyless thana quarter-wavelength, in accordance with well known transmission line.

This particular expander is described and.-

appearing in the Proceedings of the Instituteof Radio Engineers, October 1959, pages 17-13 to 17-23, and is described and claimed in the previously mentioned copending applications of Adler and applications therein mentioned. Reference .to such literature may be had for further details. 7

A principal feature of this invention resides in the coupling system which is utilized for coupling energy. of a predetermined frequency from coupler 13 to an external.

circuit. From a broad standpoint, signal energy is transferred between the electron beam and twisted helices 32,1 33 which have a predetermined capacitive reactance- This reactance is dependent on their physical configuration and the operating frequency. Coupling structure 32, 33 is resonant at this predetermined frequency and the inductive portion of the resonant circuit is supplied by support frames 35 and 37 and cross elements 38 and 39.

The equivalent electrical circuit of the frame structure is illustrated by the circuit schematic in FIGURE 5. In

Each of transmission lines a, b, c, and d may be thought of as a quarter-wavelength stub which is terminated in a short circuit consisting of element 38' or 39. In order to present an inductive ,reactance at the terminals' of coupler strips 32, 33, the electrical length of the transtheory; The parallel, combination of the inductances of each transmission line produces an equivalent inductive reactance connected to coupling structure 32,, .33 for placing the coupler in a resonantcoudition at its operating frequency. Short circuitelements 38zand 39in-- herently carry relatively high current and thus produce a magnetic field substantially stronger than elsewhere along the transmission lines.

Common elements 38 and 39 are placed in 'close pr0x-' imity to envelope 10 in order to facilitate the coupling of signal energy to an external circuit. The relatively large magnetic field producedby these elements enhances the magnetic coupling to the inductive member. situated outside of the tube envelope- More specifically, signal energy. is transferred from common element 38 to external signal circuitry outside of envelope 10 by means of a coupling assembly 55 as shown in FIGURE 4. As shown in FIG-, URE 1, assembly 55 includes an inductivemember 57" which is located directly above element 38 and coupler section 13 outside of the envelope. The details of this,

coupling assembly are described in copending application of Adler et al., Serial No. 74,084, filed December 6, 1960,

entitled, Parametric Amplifier Tube, andassigned to the same assiguee as the presentinvention;

Signals are conveyed into or out of coupling assembly 55 from a shielded conductor 56. Carried at the terminating end of conductor 56 is a coupling circuit having the inductive member 57 which is a metal conductive strip comparable in size, shape and alignment to inductive element 38. A hollow shaft 58 is threaded into assembly 55 and encompasses an electrode 59 attached toinductor vances or retracts the shaft to. vary the capacitance. As

explained in the above-mentioned Adler application,cou-' pling between inductor member 57 and inductive element 38 is optimized by adjustment of shaft 58 and the over-- all location of assembly 55 on the envelope. External coupling could also extend simultaneously to common. element 39. ifbandwidth requirementsmade this neces sary.

In order more clearly to illustrate the problem which the claimed structure solves, a short discussion follows on the design requirements of a coupler of the present type. The strips 32, 33,,which as mentioned above form a coupler for interaction with the electron beam, constitute a lumped capacity. The desired .aimis to tune this capacity to the center of the operating frequency band which, of course, calls for a specific inductance, At the same time, a means of coupling energy to an external value of inductance required would normally have a single turn. In going to higher and higher frequencies,

however, the capacity of the active coupler elements surrounding the beam cannot be reduced without limit and, therefore, the physical size of the required tuning inductmember, 57 to form a capacitor. Rotation of shaft-58 ad-' T ance shrinks as frequencies are increased. For example, the size may become so small that even a single turn inductive loop is unable to reach the glass envelope. Since it also is desired to couple to the loop inductively from the outside, the magnetic field of the loop should be concentrated near the envelope; this would require long leads of negligible inductance between the center of the tube and the envelope. Such leads can be realized in the form of large area strips closely spaced, but such strips would have large capacity, thereby defeating the original intent to reduce the required tuning inductance. Thus, to restate the problem in its clearest possible form, the requirements of concentrating the magnetic field of the tuning inductance near the glass envelope and of maintaining inductance as well as capacity sufiiciently low to operate at frequencies as, for example, in the two kilo-megacycle region, are mutually contradictory.

The structure according to this invention overcomes this difliculty by not only using a number of inductive transmission lines in parallel, but by so combining the short circuited ends of pairs of these lines that a high magnetic field is generated in the vicinity of the combined ends. By paralleling a number of larger inductances this permits the use of structures long enough to reach the envelope; at the same time the largest magnetic field is in the vicinity of the short and the shorts of at least two transmission lines are combined to obtain a high magnetic field which may easily be coupled to an external circuit.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. An electron coupling system comprising;

an envelope of low magnetic loss material;

an electron source for projecting an electron beam along a predetermined path within said envelope;

a coupler having a predetermined reactance disposed in said envelope along said path for transferring energy of a predetermined frequency between said beam and said coupler;

a plurality of transmission lines each with one end electrically connected to said coupler, the other end of at least two of said lines terminating in a common inductive element thereby producing a magnetic field substantially stronger than elsewhere along said transmission lines, said element being positioned in close proximity to said envelope, and said transmission lines having respective lengths which produce an equivalent reactance at said ends connected to said coupler for placing said coupler in a resonant condition at said frequency;

and means having an inductive member situated outside of said envelope for coupling to said magnetic field of said common element for inductively transferring energy at said frequency between said common element and said inductive member through said envelope.

2. An electron coupling system comprising:

an envelope of low magnetic loss material;

an electron source for projecting an electron beam along a predetermined path within said envelope;

an elongated coupling structure including two pairs of terminals near opposed ends of said structure and having a predetermined capacitive reactance disposed in said envelope along said path for transferring energy of a predetermined frequency between said beam and said coupler;

a pair of balanced transmission lines each with one end respectively attached to said two pairs of terminals and with the lines being joined together at their other ends and equipped with a common short circuit element, said balanced transmission lines having respec-' tive lengths which produce an equivalent inductive reactance at said ends connected to said coupling structure for placing said coupler in a resonant condition at said frequency;

and means having an inductive member situated outside of said envelope for inductively transferring energy at said frequency between said common element and said inductive member through said envelope.

3. A11 electron coupling system comprising:

an envelope of low magnetic loss material;

an electron source for projecting an electron beam along a predetermined path within said envelope;

an elongated coupling structure including two pairs of terminals near opposed ends of said structure and having a predetermined capacitive reactance disposed in said envelope along said path for transferring energy of a predetermined frequency between said beam and said coupler;

a first pair of balanced transmission lines'each with one end respectively attached to said two pairs of terminals and with said lines being joined together at their other ends and equipped with a first common short circuit element;

a second pair of balanced transmission lines each with one end respectively attached to said two parts of terminals and with said lines being joined together at their other ends and equipped with a second common short circuit element, said first and second pair of balanced transmission lines having respective lengths which produce an equivalent inductive reactance at said ends connected to said coupling structure for placing said coupler in a resonant condition at said frequency;

and means having an inductive member situated outside of said envelope for inductively transferring energy at said frequency between at least one of said common elements and said inductive member through said envelope.

References Cited by the Examiner UNITED STATES PATENTS 2,846,613 8/1958 Pierce 3153.6 2,945,155 7/1960 Chadorow 3l55.39 3,179,895 4/1965 Adler et a1. 330-43 HERMAN KARL SAALBACH, Primary Examiner.

R. D. COHN, Assistant Examiner. 

1. AN ELECTRON COUPLING SYSTEM COMPRISING: AN ENVELOPE OF LOW MAGNETIC LOSS MATERIAL; AN ELECTRON SOURCE FOR PROJECTING AN ELECTRON BEAM ALONG A PREDETERMINED PATH WITHIN SAID ENVELOPE; A COUPLER HAVING A PREDETERMINED REACTANCE DISPOSED IN SAID ENVELOPE ALONG SAID PATH FOR TRANSFERRING ENERGY OF A PREDETERMINED FREQUENCY BETWEEN SAID BEAM AND SAID COUPLER; A PLURALITY OF TRANSMISSION LINES EACH WITH ONE END ELECTRICALLY CONNECTED TO SAID COUPLER, THE OTHER END OF AT LEAST TWO OF SAID LINES TERMINATING IN A COMMON INDUCTIVE ELEMENT THEREBY PRODUCING A MAGNETIC FIELD SUBSTANTIALLY STRONGER THAN ELSEWHERE ALONG SAID TRANSMISSION LINES, SAID ELEMENT BEING POSITIONED IN CLOSE 